1. Field of the Invention
The present invention relates to a mark position detecting apparatus that detects, for instance, the position of a test mark on a substrate and, more specifically, it relates to a mark position detecting apparatus ideal for highly accurate position detection which may be performed during the process of manufacturing semiconductor elements or the like.
2. Description of the Related Art
As is known in the related art, when manufacturing a semiconductor element or a liquid crystal display element, a circuit pattern is transferred onto a film constituted of a specific material set directly under and adjacent to a resist film (a pattern formation process) by transferring the circuit pattern onto the resist film (resist pattern) through an exposure step during which the circuit pattern formed at a mask (a reticle) is imprinted on the resist film and a development step during which exposed portions or unexposed portions of the resist film are dissolved and then by performing etching, vapor deposition or the like with the resist pattern acting as a mask (a processing step).
Next, a similar pattern formation process is repeated in order to form another circuit pattern over the circuit pattern formed at the film constituted of the specific material. By repeatedly executing the pattern formation process numerous times, circuit patterns transferred onto films constituted of various materials are laminated on the substrate (a semiconductor wafer or a liquid crystal substrate), and thus, a semiconductor element circuit or a liquid crystal display element circuit is formed.
During the manufacturing process described above, the mask and the substrate are aligned with each other prior to the exposure step and the state of the registration of the resist pattern on the substrate is inspected after the development step and prior to the processing step in each pattern formation process so as to ensure that the circuit patterns at the films constituted of various materials are registered with precise alignment and ultimately to improve the product yield.
It is to be noted that the alignment of the mask and the substrate (executed prior to the exposure step), during which the circuit pattern on the mask and the circuit pattern formed on the substrate through the immediately preceding pattern formation process are aligned with each other, is executed by using marks indicating reference positions of the individual circuit patterns.
In addition, the inspection of the state of the registration of the resist pattern on the substrate (executed prior to the processing step), during which the state of registration of the resist pattern relative to the circuit pattern formed through the immediately preceding pattern formation process (hereafter referred to as a “base pattern”) is inspected, is executed by using marks indicating reference positions of the base pattern and the resist pattern.
The positions of the marks used in the alignment and the registration state inspection are detected by capturing images of the marks with an image capturing element such as a CCD camera and executing image processing on the image signals thus obtained.
However, distortion manifests in the image forming optical system that forms images of the marks on the image capturing surface of the image capturing element in the mark position detecting apparatus in the related art described above, which leads to a failure in detecting the mark positions with accuracy. At present, it is difficult to completely eliminate this distortion.